[libc++] Guard __cpp_lib_constexpr_dynamic_alloc with compiler support

[ldionne]

Summary

This fix test failures in std/utilities/memory with Clang 8. Clang 8
supports the -std=c++2a flag, but does not implement
__cpp_constexpr_dynamic_alloc, so we get errors when evaluating some static
asserts in these test files.

I am not sure if the library version macro needs to depend on compiler
support, but some of the other macros already do this.

[arichardson]

• allocate_hint.pass.cpp also fails with clang 10: https://godbolt.org/z/7aKon9

[ldionne]

Thanks for looking into this. I just recently hacked up something to silence these failures on the Clang 8 builders, but I think this is better.

However, the tests like libcxx/test/std/language.support/support.limits/support.limits.general/memory.version.pass.cpp are auto-generated. You need to modify libcxx/utils/generate_feature_test_macro_components.py instead.

[arichardson]

In D91154#2408774, @ldionne wrote:

Thanks for looking into this. I just recently hacked up something to silence these failures on the Clang 8 builders, but I think this is better.

However, the tests like libcxx/test/std/language.support/support.limits/support.limits.general/memory.version.pass.cpp are auto-generated. You need to modify libcxx/utils/generate_feature_test_macro_components.py instead.

Will do. I clearly can't read, it even says so in the first few lines of that file...

[arichardson]

• update the script instead

[ldionne]

libcxx/test/std/utilities/memory/allocator.traits/allocator.traits.members/construct.pass.cpp

175 ↗

(On Diff #308091)

Same as below.

libcxx/test/std/utilities/memory/allocator.traits/allocator.traits.members/destroy.pass.cpp

134

I'd much rather keep this conditioned on TEST_STD_VER. Otherwise, we're assuming that __cpp_constexpr_dynamic_alloc is defined properly, else this will never get tested.

This shouldn't be an issue since the test is disabled with older Clangs anyway.

libcxx/test/std/utilities/memory/default.allocator/allocator.members/allocate.pass.cpp

83 ↗

(On Diff #308091)

Same.

[arichardson]

rebase

libcxx/utils/generate_feature_test_macro_components.py

1

I made this change because running the script failed with python2.7

[ldionne]

I'm not a big fan of making __cpp_lib_constexpr_dynamic_alloc depend on __cpp_constexpr_dynamic_alloc. I'd rather we assume the compiler provides the right support when C++20 is enabled, since this simplifies everything. But since we currently claim to support older compilers, let's make this change.

[ldionne]

Abandoning since we don't support Clang 8 anymore.

libcxx/include/version

 #   define __cpp_lib_atomic_wait                        201907L
 # endif
 // # define __cpp_lib_bind_front                           201811L
 // # define __cpp_lib_bit_cast                             201806L
 # if !defined(_LIBCPP_NO_HAS_CHAR8_T)
 #   define __cpp_lib_char8_t                            201811L
 # endif
 // # define __cpp_lib_concepts                             201806L
-# define __cpp_lib_constexpr_dynamic_alloc              201907L
+# if defined(__cpp_constexpr_dynamic_alloc)
+#   define __cpp_lib_constexpr_dynamic_alloc            201907L
+# endif
 # define __cpp_lib_constexpr_functional                 201907L
 # define __cpp_lib_constexpr_numeric                    201911L
 // # define __cpp_lib_constexpr_swap_algorithms            201806L
 # define __cpp_lib_constexpr_utility                    201811L
 # if _LIBCPP_STD_VER > 17 && defined(__cpp_impl_destroying_delete) && __cpp_impl_destroying_delete >= 201806L
 #   define __cpp_lib_destroying_delete                  201806L
 # endif
 # define __cpp_lib_endian                               201907L

libcxx/test/std/language.support/support.limits/support.limits.general/memory.version.pass.cpp

 #     error "__cpp_lib_atomic_value_initialization should have the value 201911L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_atomic_value_initialization
 #     error "__cpp_lib_atomic_value_initialization should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
-# ifndef __cpp_lib_constexpr_dynamic_alloc
-#   error "__cpp_lib_constexpr_dynamic_alloc should be defined in c++20"
-# endif
-# if __cpp_lib_constexpr_dynamic_alloc != 201907L
-#   error "__cpp_lib_constexpr_dynamic_alloc should have the value 201907L in c++20"
-# endif
+# if defined(__cpp_constexpr_dynamic_alloc)
+#   ifndef __cpp_lib_constexpr_dynamic_alloc
+#     error "__cpp_lib_constexpr_dynamic_alloc should be defined in c++20"
+#   endif
+#   if __cpp_lib_constexpr_dynamic_alloc != 201907L
+#     error "__cpp_lib_constexpr_dynamic_alloc should have the value 201907L in c++20"
+#   endif
+# else
+#   ifdef __cpp_lib_constexpr_dynamic_alloc
+#     error "__cpp_lib_constexpr_dynamic_alloc should not be defined when defined(__cpp_constexpr_dynamic_alloc) is not defined!"
+#   endif
+# endif
 
 # ifndef __cpp_lib_enable_shared_from_this
 #   error "__cpp_lib_enable_shared_from_this should be defined in c++20"
 # endif
 # if __cpp_lib_enable_shared_from_this != 201603L
 #   error "__cpp_lib_enable_shared_from_this should have the value 201603L in c++20"
 # endif
 

libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp

 #     error "__cpp_lib_concepts should have the value 201806L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_concepts
 #     error "__cpp_lib_concepts should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
-# ifndef __cpp_lib_constexpr_dynamic_alloc
-#   error "__cpp_lib_constexpr_dynamic_alloc should be defined in c++20"
-# endif
-# if __cpp_lib_constexpr_dynamic_alloc != 201907L
-#   error "__cpp_lib_constexpr_dynamic_alloc should have the value 201907L in c++20"
-# endif
+# if defined(__cpp_constexpr_dynamic_alloc)
+#   ifndef __cpp_lib_constexpr_dynamic_alloc
+#     error "__cpp_lib_constexpr_dynamic_alloc should be defined in c++20"
+#   endif
+#   if __cpp_lib_constexpr_dynamic_alloc != 201907L
+#     error "__cpp_lib_constexpr_dynamic_alloc should have the value 201907L in c++20"
+#   endif
+# else
+#   ifdef __cpp_lib_constexpr_dynamic_alloc
+#     error "__cpp_lib_constexpr_dynamic_alloc should not be defined when defined(__cpp_constexpr_dynamic_alloc) is not defined!"
+#   endif
+# endif
 
 # ifndef __cpp_lib_constexpr_functional
 #   error "__cpp_lib_constexpr_functional should be defined in c++20"
 # endif
 # if __cpp_lib_constexpr_functional != 201907L
 #   error "__cpp_lib_constexpr_functional should have the value 201907L in c++20"
 # endif
 

libcxx/test/std/utilities/memory/allocator.traits/allocator.traits.members/allocate.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
+// constexpr bool test() results in "error: constexpr function never produces a
+// constant expression" before clang 11
+// UNSUPPORTED: clang-5, clang-6, clang-7, clang-8, clang-9, clang-10
 // UNSUPPORTED: gcc-8, gcc-9
 
 // <memory>
 
 // template <class Alloc>
 // struct allocator_traits
 // {
 //     static constexpr pointer allocate(allocator_type& a, size_type n);

libcxx/test/std/utilities/memory/allocator.traits/allocator.traits.members/allocate_hint.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: clang-8
+// constexpr bool test() results in "error: constexpr function never produces a
+// constant expression" before clang 11
+// UNSUPPORTED: clang-5, clang-6, clang-7, clang-8, clang-9, clang-10
 // UNSUPPORTED: gcc-8, gcc-9
 
 // <memory>
 
 // template <class Alloc>
 // struct allocator_traits
 // {
 //     static constexpr pointer allocate(allocator_type& a, size_type n, const_void_pointer hint);

libcxx/test/std/utilities/memory/allocator.traits/allocator.traits.members/destroy.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: clang-8
+// constexpr destructors are only supported starting with clang 10
+// UNSUPPORTED: clang-5, clang-6, clang-7, clang-8, clang-9
 // constexpr destructors are only supported starting with gcc 10
 // UNSUPPORTED: gcc-8, gcc-9
 
 // <memory>
 
 // template <class Alloc>
 // struct allocator_traits
 // {
TEST_CONSTEXPR_CXX20 bool test()
         std::allocator_traits<Alloc>::deallocate(alloc, pool, 1);
     }
     return true;
 }
 
 int main(int, char**)
 {
     test();
 #if TEST_STD_VER > 17
     static_assert(test());
 #endif
     return 0;
 }

libcxx/utils/generate_feature_test_macro_components.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import os
-from builtins import range
 from functools import reduce
 
 def get_libcxx_paths():
   utils_path = os.path.dirname(os.path.abspath(__file__))
   script_name = os.path.basename(__file__)
   assert os.path.exists(utils_path)
   src_root = os.path.dirname(utils_path)
   include_path = os.path.join(src_root, 'include')
feature_test_macros = [ add_version_header(x) for x in [
     "headers": ["complex"],
   }, {
     "name": "__cpp_lib_concepts",
     "values": { "c++20": 201806 },
     "headers": ["concepts"],
     "unimplemented": True,
   }, {
     "name": "__cpp_lib_constexpr_dynamic_alloc",
+    "depends": "defined(__cpp_constexpr_dynamic_alloc)",
+    "internal_depends": "defined(__cpp_constexpr_dynamic_alloc)",
     "values": { "c++20": 201907 },
     "headers": ["memory"],
   }, {
     "name": "__cpp_lib_constexpr_functional",
     "values": { "c++20": 201907 },
     "headers": ["functional"],
   }, {
     "name": "__cpp_lib_constexpr_numeric",